Unfortunately there is a number of different causes of popeye ranging from trauma damage to bad water quality any number of different type infections and it is very difficult to tell which it is and therefor it is difficult to treat.. If it is only one eye it is likely just trauma damage. Regardless, you want to keep the water extra clean. You can add maybe a tablespoon of epsom salt/5 gallons to try and reduce the fluids in the eye. If this is not working next you would want to dose antibiotics, tetracycline I believe works well, make sure to use it in a quarantine tank, not your main tank. Last would be to treat for parasites.

Your betta had popeye and dropsy, and you blame her death on a wolf spider? :/

Anyway, I agree with JorgeBurrito's post--hopefully the epsom salt will have a positive effect. If you tell us more details about the fish's living situation we might be able to determine possible causes for his condition. You can start by filling out the answers to these questions: http://www.bettafish.com/showthread.php?t=49233